The present invention relates to a method of manufacturing a temperature sensor for detecting a temperature by utilizing a thermistor element disposed inside a metal tube particularly for detecting an exhaust gas temperature of a vehicle and also relates to a temperature sensor manufactured thereby.
As a prior art, there is provided, for example, Japanese Patent Laid-open (KOKAI) Publication No. HEI 10-318850 which shows a temperature sensor in which a temperature detecting element having an electrode wire is disposed in a bottomed cylindrical metal tube for detecting an exhaust gas temperature of a vehicle, for example. More in detail, in this example, a temperature sensor has a metal cap usable at a temperature of more than 1000xc2x0 C., and inside the cap, there is disposed a temperature detecting element so as not to be directly exposed to reducing atmosphere due to oxidation of an inside surface of the cap.
In the temperature detecting device of the structure mentioned above, a coating film is formed to an inside surface of the bottomed end portion of the cap. This coating film is formed of an inorganic oxide and the temperature detecting element is inserted in such metal cap.
By the way, when it has been required to reduce a diameter of the metal tube to improve response time or responsibility of the temperature sensor, a clearance between the inner peripheral surface of the metal tube and the outer peripheral surface of the thermistor element becomes reduced. In the case of small clearance, there may cause a fear or defect that the thermistor element contacts the inner peripheral surface of the metal tube at the time of insertion of the thermistor element into the metal tube, the electrode wire of the thermistor element is engaged with the metal tube due to sliding resistance therebetween and then bent, and therefore, it becomes difficult to insert the theremistor element to the bottom portion of the metal tube. As a result, the arrangement of the thermistor element in the metal tube becomes irregular and, due to such irregularity of the arrangement of the thermistor element, constant measurement precision cannot be achieved.
The present invention was conceived in consideration of the defects or drawbacks encountered in the prior art mentioned above and an object of the present invention is, therefore, to provide a method of manufacturing a temperature sensor, in which a thermistor element is disposed in a bottomed cylindrical metal tube, capable of substantially eliminating unevenness in measurement precision and also to provide a temperature sensor having an improved structure manufactured by the method mentioned above.
This and other objects can be achieved according to the present invention by providing, in one aspect, a method of manufacturing a temperature sensor which comprises a bottomed metal tube and a thermistor element inserted into the metal tube, comprising the steps of:
preparing a metal tube and a thermistor element; and
inserting the thermistor element into the metal tube while filling an inside of the metal tube with a filler material to reduce a sliding resistance between the thermistor element and the metal tube.
In another aspect of the present invention, there is provided a method of manufacturing a temperature sensor which comprises a bottomed metal tube and a thermistor element inserted into the metal tube, comprising the steps of:
preparing a metal tube and a thermistor element;
positioning an insertion side front end of the thermistor element to an open end portion of the metal tube;
filling an inside of the metal tube with a filler material through a clearance between the front end of the thermistor element and the metal tube to reduce a sliding resistance between the thermistor element and the metal tube; and
inserting the thermistor element into the metal tube.
In a further aspect of the present invention, there is also provided a method of manufacturing a temperature sensor which comprises a bottomed metal tube and a thermistor element inserted into the metal tube, comprising the steps of:
preparing a metal tube and a thermistor element;
filling an inside of the metal tube with a filler material;
positioning an insertion side front end of the thermistor element to an open end portion of the metal tube; and
inserting the thermistor element into the metal tube while further filling the inside of the metal tube with the filler material through a clearance between the front end of the thermistor element and the metal tube to reduce a sliding resistance between the thermistor element and the metal tube.
Preferred examples of the above aspects may provide the following features or characters.
The filler material is a silicone oil. The silicone oil has a viscosity of 100 to 1500 cmxc2x7stokes, preferably of 500 to 800 cmxc2x7stokes.
The metal tube has an outer diameter of 0.5 to 1.5 mm.
An ambient temperature of a portion to be detected is xe2x88x9240 to 1000xc2x0 C.
The metal tube has a depth of 5 to 25 mm from an opened end of the bottomed metal tube to the bottom portion thereof.
Furthermore, the filler material is a silicone oil and the metal tube is heated after the insertion of the thermistor element thereinto so as to volatilize an oil component of the silicone oil.
Still furthermore, the filler material is a silicone oil, ceramics powder is mixed with the silicone oil and the metal tube is heated after the insertion of the thermistor element thereinto so as to volatilize an oil component of the silicone oil and to sinter the ceramics powder to thereby secure the thermistor element to the metal tube.
In a detailed aspect of the present invention, there is provided a method of manufacturing a temperature sensor which comprises a bottomed metal tube and a thermistor element inserted into the metal tube, comprising the steps of:
preparing a metal tube and a thermistor element provided with an electrode wire from which a lead wire extends, a terminal being connected to the lead wire;
inserting the thermistor element into the metal tube while filling an inside of the metal tube with a filler material, preferably of silicone oil, to thereby form an integral structure of the metal tube and the thermistor element;
mounting the integral structure to a housing from which the bottomed end portion of the metal tube extends outward; and
feeding an electrical insulating material into the housing.
In the other aspect, the present invention provides a temperature sensor comprising:
a bottomed metal tube;
a thermistor element provided with an electrode wire from which a lead wire extends, the thermistor element being inserted into the metal tube;
a terminal electrically connected to the lead wire;
a filler, preferably a silicone oil, charged into the metal tube, the metal tube, the thermistor element and the filler being formed into an integral structure; and
a housing into which the integral structure is mounted so that the bottomed end portion of the metal tube extends outward the housing.
According to the preferred embodiments or examples of the characters mentioned above, since the filler, preferably of silicone oil, is applied between the metal tube and the thermistor element, the sliding resistance can be made at the time of insertion of the thermistor element into the metal tube smoothly to the bottom portion thereof, thus improving the temperature measuring performance, for example, of an exhaust gas of a vehicle.
The insertion of the filler beforehand the insertion of the thermistor element into the metal tube can enhance the smooth and accurate insertion thereof.
In the preferred embodiment, when the metal tube is heated after the insertion of the thermistor element with the silicone oil, the oil component of the silicone oil volatilized and only the solid silica powder remains in the metal tube, whereby the leakage of liquid component during the use of the temperature sensor can be prevented.
Furthermore, by mixing the ceramics powder with the silicone oil and sintering the ceramics powder, the thermistor element can be effectively secured to the metal tube.
The temperature sensor manufactured by the method of the present invention can achieve the improved temperature detection function.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.